This invention relates generally to energy detection systems and more particularly to energy detection systems disposed on a single crystal substrate.
As is known in the art, electromagnetic energy detection systems have a wide range of application, e.g. from cameras to missile seekers. In such systems, electromagnetic energy, e.g., visible light or infrared energy, is focused by an optical system onto one, or more, electromagnetic energy detectors. These detectors are often arranged in an array which is disposed at the focal plane of the optical system. The detector produces an indication of the detected energy by, for example, producing a corresponding electrical output signal. In one focal plane array, the detectors are semiconductor devices, such as HgCdTe or InSb, formed in different isolated regions of an upper surface of a single crystal semiconductor body. Thus, in response to light impinging upon the detector, charge is produced in the corresponding isolated region of the semiconductor body having the detector.
In one system, a read-out electronics ("ROE"), formed as an integrated circuit in a second semiconductor substrate, typically silicon, is mounted to a back surface of the first-mentioned substrate. The charge produced in the first-mentioned substrate passes to different isolated regions of the second-mentioned substrate through electrical contacts disposed therebetween. The read-out electronics provides clock signals to regulate the propagation of charge in the second-mentioned substrate to output signal processing circuitry. In order to transfer the charge produced in the first-mentioned substrate to the second substrate, a wire or other metal contacts are connected to ohmic contact diffusion regions in the semiconductor bodies to provide electrical contact. The ohmic contact regions result in the generation of generation-recombination (GR) noise. While this technique may be acceptable for some wavelengths of energy, the GR noise produced may create, in some applications, an unacceptably low signal to noise ratio (SNR) for some combinations of wavelength and substrate.
The use of a single silicon substrate for both the detectors and the read-out electronics has been suggested. However, with a silicon substrate, near infrared energy above about 8,000 .ANG. passes readily through the substrate without generating sufficient charge for system SNR requirements. One technique has been presented in two articles, one entitled "Active-Pixel Image Sensor Integrated With Readout Circuits," by Robert Nixon, Eric Fossum, and Sabrina Kemeny and the other entitled "CMOS Active-Pixel Image Sensor Containing Pinned Photodiodes," by Eric R. Fossum both published in NASA Tech Briefs, October, 1996, from NASA's Jet Propulsion Laboratory in Pasadena, Calif. In the articles, the authors describe an attempt at an image sensor including readout circuits and pinned diode detectors, for visible and ultraviolet light, on one chip. According to the second-mentioned article, however, the operation of the device has not been demonstrated.